A curable composition having an acrylic functional group, particularly an anaerobic curable composition, uses a (meth)acrylic acid ester monomer as a main component and has a property that as long as it is contacted with air or oxygen (hereinafter, simply referred to as air), the composition is stably held in a liquid state for a long period of time with no occurrence of gelling and is rapidly cured when air is blocked or eliminated, and by making use of such a property, the composition has been used, for example, for adhesion or fixing of a screw, a bolt or the like, fixing of a mating component, adhesion between flange surfaces, or filling of a hole formed in a seal or a cast component.
The anaerobic curable composition exhibits rapid curability at ordinary temperature and keeps stable physical properties even after curing and therefore, its utilization for electrical/electronic components and the like is recently increasing. Particularly, in the field of motors, from the standpoint of productivity, an anaerobic curable composition combined with a curing accelerator is used, for example, for adhesion of a bearing and its shaft or fitting and adhesion of a peripheral portion thereof (see, for example, Patent Document 1).
While the above-described characteristics are known, the anaerobic curable composition has a problem that an outgas derived from a low-molecular volatile acrylic monomer contained in a raw material causes contamination of a substrate. Particularly, in the case where the substrate is an electrical/electronic component, the contaminated part may affect the quality of the final product, and attempts have been heretofore made to reduce the outgas. Examples thereof include a method of reducing the amount added of a volatile acrylic monomer that works out to a main component of the outgas, and blending a polyfunctional acrylate, and a method of blending a peroxide that undergoes rapid thermal decomposition, thereby swiftly consuming an unreacted volatile acrylic monomer.
In addition, there have been proposed techniques of, for example, blending a glycidyl group-containing compound and an amine compound in an anaerobic curable composition (Patent Document 2) or further imparting ultraviolet curability to an anaerobic curable composition having a high glass transition temperature (Patent Document 3).